1. Technical Field
This invention generally relates to a signal converter for converting signals transmitted from a Universal Serial Bus conforming to standards, as implemented by the Universal Serial Bus Implementation Forum, to signals transmitted from a parallel port conforming to IEEE Standard 1284 and the reverse.
2. Background
Throughout its history, the computer and computer peripheral electronics industry has made a continuing effort to standardize input/output ports and signal or communication protocols. This has been, in large part, accomplished by adoption and adherence to industry standards such as those set forth by the Institute of Electrical and Electronic Engineers (IEEE).
A number of computer peripherals, including most printing devices, some paper and photograph scanners, and also some peripheral memory storage devices, are designed for interconnection to a host computer through the standard, and well known parallel port connector which conforms to the IEEE 1284 standard as adopted in the fall of 1994.
With printers, the typical information flow and processing steps can be demonstrated by simple example as follows: The document to be printed is first generated in the host computer using information processing application software, such as a word processing, or a spread sheet, program. The document, in the form of an electronic file of information, is then processed in a second software program, usually called a printer driver, where the information from the original application file is converted into a string of data bits which will ultimately be used by the printer to generate pixels in the complete dithered printed image. The printer driver software will perform such functions as scaling of pixels, addressing, adding color data, and often times even compressing the data in the event of redundant data.
This data stream is then passed through a third, lower level driver software application, usually the operating system software, where it is assembled into bytes suitable for transmission through the host computer's parallel port to the computer peripheral, which in this example is a printer. Over the years, a number of communication protocols have been developed for use in communication between the host computer and the printer peripheral. The earliest and simplest of these protocols is known as the compatibility mode protocol, in which data is sent from the host computer to the printer in one direction only, in eight bit, or one byte, parallel format. A more advanced version of compatibility mode includes what is known as the NIBBLE mode protocol which provides or allows specific information to flow back from the printer to the host computer over dedicated pins of the parallel port, four bits at a time, and enables the printer to report to the host computer status conditions.
Still later, the Extended Capabilities Port (ECP) protocol was developed wherein eight bits, one byte, of information can flow in either direction between the host computer and the peripheral printer. Another protocol, known as the Enhanced Parallel Port (EPP) protocol permits simultaneous transmission of a byte of information in both directions between the host computer and the printer.
The vast majority of printers of whatever type, make and manufacture, that are in use and are currently being manufactured in the United States, are for use with one or more of these communications protocols in conjunction with a parallel port conforming to the IEEE 1284 standard.
Other computer peripherals, including document scanners and peripheral memory storage devices, also utilize the parallel port conforming to the IEEE 1284 standard, and these communications protocols. However, because of the differing requirements, there may be additional protocols built into the peripheral driver resident in the host which are not standard in compatibility mode, enhanced capabilities port mode, or in the extended parallel port mode.
The Universal Serial Bus, USB, communication protocol is different in some fundamental areas, not the least of which is USB is a serial communications protocol, which is designed around shift registers. As a result, it is not possible to connect the input/output, I/O, USB port to a device designed to receive and transmit data through an I/O parallel port conforming to the IEEE 1284 standard. Accordingly, what is needed is a device which can be used to connect a USB ported host to a peripheral as a parallel ported, IEEE 1284 conforming, host. It is one object of this invention to provide a converter which can operate in an automatic mode as a fully compliant USB device receiving and sending data using USB communications protocols, and as a re-transmitting device sending and receiving data to an attached peripheral device as a fully compliant parallel port device, all done in a transparent manner wherein that the host need have no knowledge that the protocol translation is occurring.
It is another object of this invention to provide a signal converter which can operate in a register mode wherein the signal converter contains a set of registers which emulate those found in standard computer parallel port hardware.